The invention pertains to a heater, in particular an auxiliary heater for motor vehicles, with a burner which is located in a combustion chamber and which can be supplied with liquid fuel via a metering pump and a fuel supply line.
Heaters of the type described above, which are used as, for example, auxiliary heaters or built-in heaters in motor vehicles, are known per se. These heaters can use air or water as a heater transfer medium. Such heaters can be operated with oil, such as diesel oil, or fuel oil or motor fuel, as a fuel. There are also different types of burners, such as vaporizing burners, atomizing burners, etc.
When an air heater is installed, the fuel line between the supply unit and the heater shoulder be designed to have an inner diameter of no more than 3 mm. In order to do this, a displacement hose can be inserted into the available fuel hose over its entire length so that the clear cross-section of the fuel hose is reduced by the displacement hose for the purpose of removing bubbles of vaporized fuel from the line.
From German Auslegeschrift Pat. No. 12 41 552 a device is known for burning liquid fuel with an atomizer nozzle or vaporizor for liquid fuel that is located in the combustion chamber; this device has an adjustment unit for setting the amount of oil in the form of a handwheel which pushes a needle into the inner section of the atomizer nozzle. Such burner elements, which are referred to as injector needles and serve to regulate the supply of fuel and adjust its size, are known from, for example, German Pat. Nos. 389 199 and 551 613. The function of these needle-like elements is to ensure appropriate regulation of the amount of fuel leaving the nozzle opening by narrowing or expanding the fuel passage cross-section in front of the nozzle outlet opening.
In the heaters of the type mentioned above, it has been found that poor combustion values, with a high proportion of CO in the exhaust gas, are obtained with these heaters in the combustion mode, especially when they operate with gasoline as a fuel. In addition, erratic combustion is observed in the combustion chamber of the heater. These difficulties proved to be particularly serious when the heater had a burner which has supplied with liquid fuel via a metering pump, such as a metering reciprocating pump, and a fuel line.
The goal of the invention is, therefore, to overcome the above-mentioned problems and to refine the design of a heater of the above-mentioned type in such a way that the burner ensures even and smooth combustion in the combustion chamber and favorable combustion values are obtained with a low proportion of CO in the exhaust gas during burning.
The invention overcomes these difficulties with a heater which has a throttle in the fuel supply line between the metering pump and the burner.
Suprisingly enough, it has been found that, by providing a throttle in the fuel supply line between the metering pump and the burner in a heater of the above-mentioned type, a very simple measure makes it possible to smooth out the volume flow of fuel to the burner, and that smooth combustion in the combustion chamber and, therefore, favorable combustion values in the heater's burn mode are obtained. The throttle in the fuel supply line cushions the surging of the fuel caused by the pulsating flow of fuel being delivered. This is made possible due to the fact that the oscillatory system in the fuel supply line, with a fuel column in the line between the metering pump and the burner, is effectively damped because a narrow gap is left open between the throttle element and the inside of the fuel supply line and, when filled with fuel, this gap acts as a viscosity damper. The throttle, thus, makes it possible to decouple the oscillatory system with the oscillating fuel column. At the same time the throttle also ensures that vapor bubble formation in the fuel supply line, due to heat from the burner causing gas evolution of the fuel in the fuel supply line, is effectively suppressed; this type of vapor bubble formation can lead to additional malfunctions in the combustion mode. In particular, the throttle reduces the passage cross-section for the fuel in the fuel supply line so that the fuel is delivered to the burner more quickly and its dwell time in the fuel supply line is thus reduced. Because of the short dwell time of the fuel in the fuel supply line, gas evolution of the fuel is largely precluded. Such gas evolution is critical, especially in heaters run on gasoline since gasoline has a lower boiling point than oil. Such vapor bubble formation in the fuel supply line would also tend to amplify the oscillations of the oscillating fuel column.
The fuel supply line throttle provided in the heater of the invention, thus, performs a dual function, namely, the damping of the fuel volume flow between the metering pump and the burner and, at the same time, reduction or prevention of vapor bubble formation in the fuel supply line.
In accordance with preferred embodiments, the throttle is relatively long, i.e., the throttle elements spans a substantial extent of the fuel supply line connector. This long throttle element is preferably a wire which is mounted in the fuel line connector and which is securely connected to the burner as a permanent part of the fuel supply line. This very simple implementation of the throttle element makes it possible, surprisingly enough, to overcome all of the problems which have arisen to date with respect to fuel supply.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.